Since the introduction of parallel flow heat exchangers in 1986, their popularity has soared. Parallel flow heat exchangers, particularly when utilized as condensers or evaporators and provided with multiple flow paths of relatively small hydraulic diameter (i.e., a hydraulic diameter up to about 0.070"), have excellent efficiency. They may be readily formed of aluminum components and thus are light of weight. As such, they are ideally suited for automotive applications and provide an energy savings therein because they contribute to a reduced vehicle weight.
When used in air conditioning or refrigeration applications, they are environmentally friendly in that the heat exchangers themselves have a relatively small internal volume, thereby reducing the refrigerant charge required and thus reducing the amount of refrigerant that could be discharged to the atmosphere in the event of a system leak.
Moreover, they are readily adaptable for use with a variety of differing refrigerants, including those that pose a considerably reduced danger to the ozone layer than, for example, CFC-12.
One typical parallel flow construction is disclosed in U.S. Pat. No. 4,998,580 to Guntly, et al. From a review of that patent, it can be readily appreciated that parallel flow heat exchangers are characterized by the use of a number of tubes of flattened cross section which extend in both geometric and hydraulic parallel between two opposed headers. In some cases, baffles may be located in one or both of the headers so as to provide a multiple pass configuration, but there remains a series individual tubes of flattened cross section that extend between the headers.
Initially, and as disclosed in the '580 patent, the flattened tubes were so-called "fabricated tubes" because they were made by introducing an undulating insert into a tube of flattened cross section and bonding the insert as by brazing to both interior sides of the flattened tube. However, as recognized by Guntly in the '580 patent, extruded tubes would work equally well.
As the popularity of the parallel flow heat exchangers increased, tube extrusion techniques also improved to provide extruded tubes for use in parallel flow heat exchangers with the thought of eliminating the expense of assembling the inserts to the interior of the tubes.
That in turn led to a need for a means for cutting the extruded tube to the relative short lengths needed in assembling a parallel flow heat exchanger.
Various techniques for severing such tubing have evolved.
In U.S. Pat. No. 5,133,492 issued Jul. 28, 1992, to Wohrstein, the flattened tube is scored on opposite sides along its tube major dimension. The scoring is such that the depth of cut is less than the wall thickness of the tube at that point.
Through the use of clamping devices applied to the tubes on opposite sides of the score, a parting force is exerted on the tube. It is also possible to wiggle a free end of the tube on one side of the scoring to cause the same to break as a result of fatigue.
One difficulty with this approach is that the breaks are not particularly clean along the entirety of the tube major dimension. And as such tubes conventionally have interior webbing defining as few as two, but more likely, eight or more, discreet, interior passages of relatively small hydraulic diameter, the lack of a clean break can result in braze metal plugging or partially occluding one or more of the channels thus, obstructing flow and reducing heat transfer efficiency.
A similar approach is disclosed in U.S. Pat. No. 5,249,345 issued Oct. 5, 1993 to Virsik, et al. Virsik, rather than merely scoring the tube, actually removes metal from the tube sidewalls in forming a kerf. Through the use of clamps which are moved longitudinally away from one another, tension is placed on the tube at the kerf cause the same to rupture. Tubing cut by the Virsik method is subject to the same potential plugging problems.
Moreover, both of these methods are relatively slow in that the tube is intermittently advanced and then halted while some operation is performed on it. Consequently, production of a given number of tube lengths is unduly time consuming and, thus, expensive.
The present invention is directed to overcoming one or more of the above problems.